Endogenous Gibberellin Content Research Articles

Gibberellins involved in fruit ripening and softening by mediating multiple hormonal signals in tomato.

The phytohormone ethylene is well known for its important role in the ripening of climacteric fruit, such as tomato (Solanum lycopersicum). However, the role and mode of action of other plant hormones in climacteric fruit ripening regulation are not fully understood. Here, we showed that exogenous GA treatment or increasing endogenous gibberellin content by overexpressing the gibberellin synthesis gene SlGA3ox2 specifically in fruit tissues delayed tomato fruit ripening, whereas treatment with the GA biosynthesis inhibitor paclobutrazol (PAC) accelerated fruit ripening. Moreover, exogenous ethylene treatment cannot completely reverse the delayed fruit ripening phenotype. Furthermore, exogenous GA treatment of ethylene signalling mutant Never ripe (Nr) or SlEBF3-overexpressing lines still delayed fruit ripening, suggesting that GA involved in fruit ripening partially depends on ethylene. Transcriptome profiling showed that gibberellin affect the ripening of fruits by modulating the metabolism and signal transduction of multiple plant hormones, such as auxin and abscisic acid, in addition to ethylene. Overall, the results of this study provide new insight into the regulation of gibberellin in fruit ripening through mediating multiple hormone signals.

Influence of Seed-Covering Layers on Caper Seed Germination.

Caper is a perennial shrub that is widespread in the Mediterranean Basin. Although the fruits contain many seeds, they germinate slowly and with very low percentages, due to their nondeep physiological dormancy. The influence of the testa and endosperm, as well as the effect of applying gibberellic acid (GA3) solutions on seed germination to release its dormancy, are reported in this study. The mechanical resistance exerted by the testa and endosperm against radicle protrusion in mature caper seeds was measured. The best germination results were obtained with seeds devoid of testa wetted with water and with intact seeds wetted with a 500 mg L-1 GA3 solution, without statistical differences between them. The GA3 addition triggers an increase in both the content of endogenous gibberellins (GA) and the GA/abscisic acid ratio, increasing germination. Its germination consists of two temporally separated events: testa cracking and endosperm piercing. Testa cracking begins in the hilum-micropillar area; it involves a signal from the embryo, which GA can replace, possibly by increasing the growth potential of the embryo. After testa cracking, the radicle emerges through a hole in the micropylar endosperm. The puncture force necessary to pierce the micropylar endosperm decreased drastically during the first day of imbibition, remaining practically constant until testa cracking, decreasing afterwards, regardless of the addition or not of gibberellins.

Effects of Artificial Aging on Seed Vigor and Physiological Characteristics of the Invasive Alien Plant Aegilops tauschii

Abstract The control of invasive plants depends to some extent on the persistence of the soil seed bank. The high temperature (40 °C) accompanied with high humidity (95%) method was used to treat the seeds of the invasive species Aegilops tauschii Coss. The aim of our study was to evaluate the seed vigor and longevity by accelerating aging, to serve as a reference for the evaluation of invasion potential of A. tauschii and corresponding eradication strategy adoption. The results showed that with the extension of aging time, the germination rate (GR), energy (GE), and index (GI) of A. tauschii seeds reduced. All the results were significantly different from the control (CK) since the second day ( p < 0.05). During the aging process, the seed relative water content (RWC), relative electric conductivity (REC), and thiobarbituric acid (TBARS) level increased, while the superoxide dismutase (SOD) gradually decreased after second day of seed aging. In addition, the aging treatment also caused a continuous decrease in the endogenous gibberellin (GA 3 ) content and a continuous increase in the abscisic acid (ABA) content of the seeds. Thus, a sharp decrease in the GA 3 /ABA ratio was evident. Finally, the study revealed that the germination inhibitors of A. tauschii were mainly concentrated in the glumes, which was revealed during seed aging. The results of the comprehensive analysis indicated that the changes of the above-mentioned internal factors eventually led to a rapid decline of the seed vigor of A. tauschii . Based on the results of the aging test, and the distribution characteristics of A. tauschii seeds in the soil seed banks, we recommend that soil solarization is one of the effective methods to eradicate the seed bank of A. tauschii .

Alteration of SlYABBY2b gene expression impairs tomato ovary locule number and endogenous gibberellin content

Tomato is an ideal model species for fleshy fruit development research. SlYABBY2b regulates the ovary locule number, which is increased by gibberellins, in tomato. However, the relationship between SlYABBY2b and endogenous gibberellin is poorly understood. In this study, SlYABBY2b-overexpressing and RNA interference (RNAi) transgenic tomato plants were used to elucidate the mechanism by which SlYABBY2b regulates the ovary locule number and endogenous gibberellin content in tomato. SlYABBY2b-overexpressing plants showed fewer locules and lower gibberellin content than the control plants. Contrasting results were found in the RNAi lines. Therefore, the SlYABBY2b gene negatively regulates tomato ovary locule number and endogenous gibberellin content. Furthermore, the expression of SlYABBY2b gene was remarkably higher than that of the wild type in the apical shoots of gibberellindeficient mutants. This showed that the gibberellins can inhibit the expression of SlYABBY2b gene negative regulation. Further study revealed that SlYABBY2b suppressed the expression of SlGA20ox1 and SlGA3ox2, but increased that of SlGA2ox1 and SlGA2ox5 in the apical shoots of SlYABBY2b-overexpressing plants, thereby reducing gibberellin content. Contrasting results were found in the RNAi lines. Our results showed that the SlYABBY2b gene was located on gibberellin signal transduction pathways, fed back regulation of the synthesis of gibberellin, and felt exogenous gibberellin signal to further regulate the formation of tomato locule.

A Novel Two-Step Method for Screening Shade Tolerant Mutant Plants via Dwarfism.

When subjected to shade, plants undergo rapid shoot elongation, which often makes them more prone to disease and mechanical damage. Shade-tolerant plants can be difficult to breed; however, they offer a substantial benefit over other varieties in low-light areas. Although perennial ryegrass (Lolium perenne L.) is a popular species of turf grasses because of their good appearance and fast establishment, the plant normally does not perform well under shade conditions. It has been reported that, in turfgrass, induced dwarfism can enhance shade tolerance. Here we describe a two-step procedure for isolating shade tolerant mutants of perennial ryegrass by first screening for dominant dwarf mutants, and then screening dwarf plants for shade tolerance. The two-step screening process to isolate shade tolerant mutants can be done efficiently with limited space at early seedling stages, which enables quick and efficient isolation of shade tolerant mutants, and thus facilitates development of shade tolerant new cultivars of turfgrasses. Using the method, we isolated 136 dwarf mutants from 300,000 mutagenized seeds, with 65 being shade tolerant (0.022%). When screened directly for shade tolerance, we recovered only four mutants from a population of 150,000 (0.003%) mutagenized seeds. One shade tolerant mutant, shadow-1, was characterized in detail. In addition to dwarfism, shadow-1 and its sexual progeny displayed high degrees of tolerance to both natural and artificial shade. We showed that endogenous gibberellin (GA) content in shadow-1 was higher than wild-type controls, and shadow-1 was also partially GA insensitive. Our novel, simple and effective two-step screening method should be applicable to breeding shade tolerant cultivars of turfgrasses, ground covers, and other economically important crop plants that can be used under canopies of existing vegetation to increase productivity per unit area of land.

Diversion of carbon flux from gibberellin to steviol biosynthesis by over-expressing SrKA13H induced dwarfism and abnormality in pollen germination and seed set behaviour of transgenic Arabidopsis.

This paper documents the engineering of Arabidopsis thaliana for the ectopic over-expression of SrKA13H (ent-kaurenoic acid-13 hydroxylase) cDNA from Stevia rebaudiana. HPLC analysis revealed the significant accumulation of steviol (1-3 μg g(-1) DW) in two independent transgenic Arabidopsis lines over-expressing SrKA13H compared with the control. Independent of the steviol concentrations detected, both transgenic lines showed similar reductions in endogenous bioactive gibberellins (GA1 and GA4). They possessed phenotypic similarity to gibberellin-deficient mutants. The reduction in endogenous gibberellin content was found to be responsible for dwarfism in the transgenics. The exogenous application of GA3 could rescue the transgenics from dwarfism. The hypocotyl, rosette area, and stem length were all considerably reduced in the transgenics. A noteworthy decrease in pollen viability was noticed and, similarly, a retardation of 60-80% in pollen germination rate was observed. The exogenous application of steviol (0.2, 0.5, and 1.0 μg ml(-1)) did not influence pollen germination efficiency. This has suggested that in planta formation of steviol was not responsible for the observed changes in transgenic Arabidopsis. Further, the seed yield of the transgenics was reduced by 24-48%. Hence, this study reports for the first time that over-expression of SrKA13H cDNA in Arabidopsis has diverted the gibberellin biosynthetic route towards steviol biosynthesis. The Arabidopsis transgenics showed a significant reduction in endogenous gibberellins that might be responsible for the dwarfism, and the abnormal behaviour of pollen germination and seed set.

Effects of Gibberellin Biosynthetic Inhibitors on Oil, Secoisolaresonolodiglucoside, Seed Yield and Endogenous Gibberellin Content in Flax

Flax (Linum usitatissimum L.) has been used for the edible oil in Korea. The evaluate the effect of plant growth retardants on flaxseed yield, oil content, and gibberellin level, chloromequat chloride (CMC), paclobutrazol (PBZ), and prohexadione-Ca (PHC) were used as plant growth retardants in this study. These plant growth retardants were foliar-sprayed to flax plant at 55 days after seeding. The concentrations of each plant growth retardant were as followed: CMC 250, 500, 1000 ppm, PBZ 40, 80, 160 ppm and PHC 500, 1000, 2000 ppm. PHC treatment to forming bolls was more stimulated than CMC and PBZ. The highest ripened seed rate was observed in PHC treatment at 2000ppm. The high see yields were obtained in PHC treatment following PBZ and CMC, in turn. Seed yield that significantly increased in PBZ and PHC was found to be increased 12.4 ~ 23.9% as compared to the control. The PHC showed higher flaxseed production and oil yield than that of CMC and PBZ. The results obtained in the present study suggest that higher concentration of plant growth retardant (PHC) increased flaxseed yield and oil content. The optimal concentration of PHC treatment was observed in 2000 ppm. It concludes that the foliar application of PHC 2000 ppm may be useful for the increasing oil and higher seed production in flax plants.

Gibberellin-like substances in embryonic shoots of Scots pine in relation to generative differentiation

Investigations were carried out on embryonic shoots of lateral and terminal buds of Scots pine (<em>Pinus silvestris</em> L.) of different age. at various stages of seasonal devclopment. The results show that there is a correlation between gibberellins content and apical dominance in pine. More are found in terminal buds than in lateral ones. The transition from a juvenile phase into a mature one in Scots pine is accompanied by a lowering of the gibberellin content. The formation of male inflorescences is accompanied by an increased amount of endogenous gibberellins and the appearence of a new group of non-polar gibberellin-like substances. The formation of female cones is connected with the lowering of endogenous gibberellin content.

Heterosis in rice seedlings: its relationship to gibberellin content and expression of gibberellin metabolism and signaling genes.

Despite the accumulation of data on the genetic and molecular understanding of heterosis, there is little information on the regulation of heterosis at the physiological level. In this study, we performed a quantitative analysis of endogenous gibberellin (GA) content and expression profiling of the GA metabolism and signaling genes to investigate the possible relationship between GA signaling and heterosis for seedling development in rice (Oryza sativa). The materials used were an incomplete diallele set of 3 × 3 crosses and the six parents. In the growing shoots of the seedlings at 20 d after sowing, significant positive correlations between the contents of some GA species and performance and heterosis based on shoot dry mass were detected. Expression analyses of GA-related genes by real-time reverse transcription-polymerase chain reaction revealed that 13 out of the 16 GA-related genes examined exhibited significant differential expression among the F1 hybrid and its parents, acting predominantly in the modes of overdominance and positive dominance. Expression levels of nine genes in the hybrids displayed significant positive correlations with the heterosis of shoot dry mass. These results imply that GAs play a positive role in the regulation of heterosis for rice seedling development. In shoots plus root axes of 4-d-old germinating seeds that had undergone the deetiolation, mimicking normal germination in soil, the axis dry mass was positively correlated with the content of GA₂₉ but negatively correlated with that of GA₁₉. Our findings provide supporting evidence for GAs playing an important regulatory role in heterosis for rice seedling development.

Gibberellin retards chlorophyll degradation during senescence of Paris polyphylla

Chlorophyll (Chl) degradation was found to be related to the endogenous gibberellin (GA) content in shoots during senescence in the perennial plant Paris polyphylla var. yunnanensis (Franch.). Treatment with gibberellic acid (GA3) significantly increased the content of endogenous GAs (GA4 + GA7), retarded the senescence of shoots, and the degradation of proteins and Chl. Chlorophyllase, Mg-dechelation and peroxidase activities increased more in control plants than in those treated with GA3. GA3 treatment also protected lipoxygenase activity, which decreased significantly in control plants.

Effects of Prohexadione Calcium on growth and gibberellins contents of Chrysanthemum morifolium R. cv Monalisa White

The effect of Prohexadione Calcium (Pro-Ca) and daminozide was observed on the growth characteristics and endogenous gibberellin contents of Chrysanthemum morifolium R. cv Monalisa White. Three concentrations viz. 100, 200 and 400 ppm of Pro-Ca and a single concentration of daminozide (800 ppm) were applied three times with 7 days interval on three weeks old plant under greenhouse condition. Pro-Ca suppressed the plant length up to 30.7% while daminozide inhibited up to 27.12% at optimum concentration. The chlorophyll contents and stem diameter were higher than control, while the fresh weight and flower number insignificantly reduced with such treatments. Gibberellin (GA) analysis showed that Pro-Ca and daminozide application significantly lowered bioactive GA 1 content, although the amount of its immediate precursor GA 20 was fractionally higher. Bioactive GA 4 content was slightly higher than the control while significant difference in GA 9 was found between the plants treated with Pro-Ca and daminozide. Current study showed that both early C13 hydroxylation and non-C13 hydroxylation pathways of GA biosynthesis are operational in C. morifolium.

Inhibitory role of gibberellins in theobroxide-induced flowering of Pharbitis nil

Theobroxide, a novel active compound isolated from a fungus, has been reported previously to induce potato tuberization and flower bud formation in Pharbitis nil under non-inductive long-day conditions. Up to date, the action mechanism of theobroxide on flower-bud induction of P. nil, however, is still unknown. In the present study, we observed a reduction of the stem length, along with the induction of flower buds, in theobroxide-treated and short-day-grown P. nil plants. Also, the results showed that flower bud formation was delayed markedly in P. nil seedlings with removal of cotyledons or exposure to night break. The suppression effect of night-break and cotyledon-removal, however, was abolished completely by spraying theobroxide. Endogenous gibberellin(1/3) contents in P. nil plants treated with theobroxide or grown under short-day conditions were relatively lower, suggesting that gibberellins probably are negatively involved in theobroxide- and short-day-induced flower-bud formation of P. nil.

Ethylene Production and Endogenous Gibberellin Content in Chrysanthemum Plants as Affected by Uniconazole, Brushing and Aminoethoxyvinylglycine Treatments

Chrysanthemum (Dendranthema grandiflora (Ramat.) Kitam.) plants, sprayed with a 25 ppm uniconazole one month after planting, evolved ethylene immediately and attained the highest yield on the third day. Plants that were brushed (mechanical stress, MS) for 30 days produced more ethylene on the third day than did uniconazole-sprayed plants and maintained their high production. Plants treated with aminoethoxyvinylglycine (AVG) yielded the lowest levels of ethylene and displayed no peak. Application of AVG to uniconazole-sprayed or brushed plants decreased ethylene evolution. Gibberellic acid (GA)-like substances in the control plants separated into 4 bands on silica gel TLC plates; authentic GA1 GA3, and GA7 were detected at the same Rf in the control plants. GA1- and GA3-like substance contents decreased markedly in plants sprayed with uniconazole or brushed. The application of AVG alone did not affect GA- like substance content, nor did it enhance GA activities in uniconazole-sprayed plants. Thus, growth of chrysanthemum plants is controlled not only by GA activities but also by ethylene.

Dwarf (di)haploid pito mutants obtained from a tetraploid potato cultivar ( Solanum tuberosum subsp. tuberosum) via anther culture are defective in gibberellin biosynthesis

Nine dwarf (di)haploid lines (2 n=2×=24) were obtained from the tetraploid (2 n=4×=48), long day-adapted potato cultivar ‘Pito’ ( Solanum tuberosum subsp. tuberosum) through anther culture. They grew slowly, had very short internodes, compact and ball-shaped appearance, and dark green leaves. Dwarfism was due to a recessive gene, designated pito. Endogenous gibberellin contents were measured in the leaves of dwarf and wild-type lines by gas chromatography linked to mass spectrometry (GC-MS). High amounts of GA 19, GA 20, GA 29, GA 1, and GA 8 were detected in the wild-type plants, which indicated that the early 13-hydroxylation pathway was predominantly used for GA biosynthesis in S. t. subsp. tuberosum. Also GA 53, GA 15 and GA 9 were detected but not quantified. Very low endogenous amounts of all analysed GAs were detected in the pito mutants, indicating a block at an early part of the GA biosynthesis pathway. The dwarf lines strongly and quickly responded to the exogenous application of low amounts (79 nM) of bioactive GA (GA 3), which restored normal growth and confirmed that the pito dwarfs were synthesis mutants and not GA response mutants.

Endogenous gibberellin content does not correlate with photoperiod-induced growth changes in strawberry petioles

We have examined whether gibberellins (GAs) mediate photoperiodic growth responses in strawberry (Fragaria × ananassa) by measuring GA content and GA metabolism in petioles with accurately defined growth rates. Gibberellin A1 , GA8 , GA19 , GA20 , GA29 , GA34 , and tentatively GA17 , were identified by gas chromatography–mass spectrometry, and GA4 was detected by selected ion monitoring. Although petiole growth rates were reduced within 2 d of a long-day to short-day transfer, we found no consistent changes in GA content until 8 d, when GA1 , GA8 , GA29 and GA34 were reduced by about two-fold in short days. GA20 concentration was always low regardless of age or treatment, typically 10-fold less than GA1 and 40-fold less than GA19 . Application of paclobutrazol (25 g plant–1 ) reduced growth rate by 43%, somewhat greater than the effect of short days (23%), but resulted in a six-fold decrease in GA1 content, much greater than the maximum two-fold effect of short days. However, paclobutrazol-treated petioles in long and short days differed in growth rate by 30%, yet had no difference in GA1 content. [2H]GA19 and [2H]GA20 were metabolised to GA1 , GA8 and GA29 , although conversion of GA19 was slow. GA4 was converted to GA 34 but not to GA1 or GA8 . Photoperiod had little effect on any of these metabolic steps. For the following reasons, we suggest that the photoperiod growth response is not mediated primarily through altered GA concentrations: (1) a lack of a rapid photoperiod effect on GA concentrations or metabolism, (2) changes in growth before or independent of changes in GA concentrations and (3) a normal photoperiod effect on growth in petioles with artificially lowered GA content.

Thermoperiodic control of stem elongation and endogenous gibberellins in Campanula isophylla

The effect of day/night temperature regimes on stem elongation and on the content of endogenous gibberellins (GAs) in vegetatively propagated plants of Campanula isophylla cv. Hvit have been studied. Compared with a constant temperature regime at 18°C (18/18°C), stem and internode elongation was enhanced significantly by a combination of high day/low night temperature (21/15°C) and inhibited by an opposite regime (15/21°C). Gibberellins A1, A19, A44, A53, and A97 were identified as endogenous components in Campanula. (GA97 was earlier referred to as 2β-OH-GA53.) Quantitative analysis of the endogenous GAs indicates that temperature regimes that stimulate elongation growth are accompanied by an increase in the level of GA1, GA19, and GA44. On the other hand, in plants grown under conditions that reduced stem elongation growth, there was an increased level of GA97.

Damage of Seed Fertility by Cooling Treatment and Endogenous Gibberellins in Ears of Rice Plants(Oryza sativa L.).

葉耳間長-4から+8cmまでの穂の発育段階の異なったものを日温15℃夜温10℃の冷温で10日間処理し，その種子稔性に及ぼす影響を調べるとともに，穂の内生ジベレリン含量を調査した.冷温に遭遇させる時期が早いほど種子稔性は低下したが，品種間でその程度に差異が認められ，ササニシキの方が稔性低下が著しかった.冷温処理しないものに比較すると，冷温処理によって穂の内生ジベレリン含量は両品種ともに著しく低下したが，冷温処理下でのジベレリンの減少程度はササニシキでむしろ少なく，冷温処理しないものとの比較ではササニシキの方がジベレリンの残存する比率は大きかった.ササニシキにジベレリン生合成阻害剤のS-327Dを処理してから冷温処理を5日間処理したものでは，薬剤処理によって内生ジベレリン含量が低下すると同時に，特に葉耳間長がO～4cmの発育段階での冷温処理に対して，ジベレリン生合成阻害剤処理による種子稔性の向上が認められた.これらのことから，減数分裂期の冷温処理による種子稔性の低下には内生ジベレリンのレベルが関与している可能性が示唆される.

Vernalization and Gibberellin Physiology of Winter Canola (Endogenous Gibberellin (GA) Content and Metabolism of [3H]GA1 and [3H]GA20.

Winter canola (Brassica napus cv Crystal) is an oilseed crop that requires vernalization (chilling treatment) for the induction of stem elongation and flowering. To investigate the role of gibberellins (GAs) in vernalization-induced events, endogenous GA content and the metabolism of [3H]GAs were examined in 10-week vernalized and nonvernalized plants. Shoot tips were harvested 0, 8, and 18 d postvernalization (DPV), and GAs were purified and quantified using 2H2-internal standards and gas chromatography-selected ion monitoring. Concentrations of GA1, GA3, GA8, GA19, and GA20 were 3.1-, 2.3-, 7.8-, 12.0-, and 24.5-fold higher, respectively, in the vernalized plants at the end of the vernalization treatment (0 DPV) relative to the nonvernalized plants. Thermoregulation apparently occurs prior to GA19 biosynthesis, since vernalization elevated the concentration of all of the monitored GAs. [3H]GA20 or [3H]GA1 was applied to the shoot tips of vernalized and nonvernalized plants, and after 24 h, plants were harvested at 6, 12, and 15 DPV. Following high-performance liquid chromatography analyses, vernalized plants showed increased conversion of [3H]GA20 to a [3H]GA1-like metabolite and reduced conversion of [3H]GA1 or [3H]GA20 to polar 3H-metabolites, putative glucosyl conjugates. These results demonstrate that vernalization influences GA content and GA metabolism, with GAs serving as probable regulatory intermediaries between chilling treatment and subsequent stem growth.

Identification of Gibberellins in Spinach and Effects of Light and Darkness on their Levels

The endogenous gibberellin (GA) content of spinach (Spinacia oleracea) was reinvestigated by combined gas chromatography-mass spectrometry analysis. The 13-hydroxy GAs: GA(53), GA(44), GA(19), GA(17), GA(20), GA(5), GA(1), GA(29), and GA(8); the non-3, 13-hydroxy GAs: GA(12), GA(15), GA(9), and GA(51); and the 3beta-hydroxy GAs: GA(4), GA(7), and GA(34), were identified in spinach extracts by comparing full-scan mass spectra and Kovats retention indices with those of reference GAs. In addition, spinach plants contained GA(7)-isolactone, 16,17-dihydro-17-hydroxy-GA(53), GA(29)-catabolite, 3-epi-GA(1), and 10 uncharacterized GAs with mass spectra indicative of mono- and dihydroxy-GA(12), monohydroxy-GA(25), dihydroxy-GA(24), and dihydroxy-GA(g). The effect of light-dark conditions on the GA levels of the 13-hydroxylation pathway was studied by using labeled internal standards in selected ion monitoring mode. In short day, the GA levels were higher at the end of the light period than at the end of the dark period. Levels of GAs at the end of each short day were relatively constant. During the first supplementary light period of long day treatment, GA(53) and GA(19) declined dramatically, GA(44) and GA(1) decreased slightly, and GA(20) increased. During the subsequent high-intensity light period, the GA(20) level decreased and the levels of GA(53), GA(44), GA(19), and GA(1) increased slightly. Within 7 days after the beginning of long day treatment, similar patterns for GA(53) and GA(19) occurred. Furthermore, when these plants were transferred to darkness, an increase in the levels of GA(53) and GA(19) was observed. These results are compatible with the idea that in spinach, the flow through the GA biosynthetic pathway is much enhanced during the high-intensity light period, although GA turnover occurs also during the supplementary period of long day, both effects being responsible for the increase of GA(20) and GA(1) in long day.

Effects of gibberellin on genetic variations in α-amylase production in germinating barley seeds

For the purpose of genetically improving α-amylase production in barley malts, the relationship between endogenous gibberellin content and α-amylase activity among varieties of barley was investigated. Endogenous gibberellin content was determined by radioimmunoassay, a very sensitive assay, by which all of the so-called active gibberellins in barley were detected. Among them, GA, was the dominant endogenous gibberellin in germinating barley seeds. At 96 h after imbibition (HAI), α-amylase activities and endogenous active gibberellin contents were correlated among barley varieties. However, cv. Nijo Mochimugi had a low activity compared to endogenous gibberellin content. Interestingly, Nijo Mochimugi showed a lower response to exogenous gibberellin (we think this represents responsiveness to gibberellin in α-amylase induction: RGA) than the other varieties, strongly suggesting that the low α-amylase activity in Nijo Mochimugi resulted from the low RGA. Consequently, it is concluded that α-amylase production is affected by two factors: endogenous active gibberellin content and RGA. Variation in RGA among barley varieties was not due to differences in barley α-amylase/subtilisin inhibitor (BASI) activity. α-Amylase and protease activity induced by exogenous gibberellin were correlated, which suggests that the main mechanism(s) which causes variation in RGA would also involve protease(s) induction.